Heather Lee Robertson, 38, was indicted Thursday and faces six charges of improper relationship between educator and student and 15 charges of sexual assault. She was initially charged with four counts of improper relationship between educator and student.

KTRE reported in May that an investigation into Robertson’s relationships began on April 20 after police received a tip. One student told authorities he and a friend had a threesome with the teacher, and two other boys admitted to having sex with her multiple times. According to the affidavit, Robertson admitted to the allegations, saying she had sex with one of the students four times between late last year and this spring. The affidavit also said Robertson claimed she didn't remember the details of each instance because she had been drinking heavily.